Review my startup idea: One API to rule them all.

As far as security is concerned, you probably don't want user authentication like a username/password combo to be passed with the requests, but rather acquire an oauth token that expires after a certain period of time and have specific rights within a scope to read-only vs write based on that token.

One question with concurrent API queries is how would you handle the race condition? Say I query 3 APIs at the same time, will I have to wait until the slowest one returns the results to get all results? Will it instead push results to a pre-determined results URL?

What are some cases when you would query multiple APIs and want the results at the same time? Why not just wait for each result, parse it myself, then pass some piece of that computed result to the next query, and so on? What would be amazing would be a universal API processor that can do some of this API to API call parsing and processing in the backend, store all credentials, and just get the final results of a long chain of API calls. Now that's something that would make developers' lives easier and I'd pay money for..

Seems like it might touch on aspects of http://zapier.com which is a bit more of a mashup mentality but definitely allows you to combine multiple APIs to do interesting things.

What do you imagine this API would look like if it existed?

What use case do you believe it serves (who would use it, what existing behavior would it replace)?

If you're going to call this a "startup" then what is the business plan beyond some set of technical features which may or may not be feasible?

"One thing I haven't found, however, is one API that lets the skilled developer manipulate and search multiple APIs at once."

There is one, it is called "the internet"

See SPARQL and the semantic web, though I think the xkcd cartoon is the better response.